1. Technical Field
The invention relates to layout of a circuit board and, more particularly, to a printed circuit board and layout method thereof.
2. Description of Related Art
Printed circuit boards are designed for coupling control chips and electronic devices in two alternative modes to transmit signals such as high-speed differential signals.
Referring to FIG. 4, a commonly used printed circuit board 1 includes a pair of first transmission lines 11A, 11B, a pair of second transmission lines 12A, 12B, and a pair of third transmission lines 13A, 13B sequentially arranged thereon.
Referring to FIG. 5, in a first coupling mode, a control chip 14 is coupled to the first transmission lines 11A, 11B, and a first electronic device 15 is coupled between the second transmission lines 12A, 12B, and the first transmission lines 11A, 11B. The control chip 14 generates a pair of high-speed signals S1, S2 such as high-speed differential signals. However, a circuit stub is thus created. Referring to FIG. 6, in a second coupling mode, the control chip 14 is coupled to the first transmission lines 11A, 11B, a second electronic device 16 is coupled to ends of the third transmission lines 13A, 13B away from the control chip 14, and a pair of resistors R1, R2 must be added to connect with the second transmission lines 12A, 12B and the third transmission lines 13A, 13B. Cost of the printed circuit board 1 is increased accordingly.